1. Field of the Invention
The present invention relates to an automatic transmission and more particularly to an automatic transmission whose gear mechanism is of a conventional manual transmission.
2. Prior Art
There is a known automatic transmission having the same gear mechanism as that of a conventional manual transmission. The automatic transmission of this type has a plurality of gear trains arranged in an axial direction of the transmission and changeover mechanisms for changing gear trains. The shift change is performed by automatically controlling these changeover mechanisms by means of hydraulic pressure. This type automatic transmission has an excellent transmission efficiency of power, compared to a conventional automatic transmission primarily constituted by planetary gears, friction engagement elements (clutches, brakes) and the like. Further, since this type automatic transmission is constituted by a small number of components, it is easier to design a light weight and low cost transmission than a conventional type automatic transmission.
For example, Japanese Patent Application Laid-open No. Toku-Kai-Sho 63-2735 discloses a structure of an automatic transmission in which a sub clutch for preventing a xe2x80x9ctorque dropxe2x80x9d at shifting gears is equipped in addition to a main clutch disposed between a crank shaft of an engine and an input shaft of the transmission. This sub clutch is disposed at an end of the input shaft of the transmission. When shifting gears, the sub clutch is partially engaged by hydraulic pressure while the main clutch is held in full engagement, thereby an output torque during shifting gears is prevented from dropping abruptly and a shift shock at up-shift is alleviated. Further, automatic transmissions having similar constructions are disclosed in Japanese Patent Application Laid open No. Toku-Kai-Sho 61-45163 and Japanese Patent No. 2703169.
Further, Japanese Patent Application No. Toku-Kai-Sho 58-149443 discloses a construction in which a sub clutch is disposed on an axis of a counter shaft provided in parallel with an input shaft and an output shaft of the transmission. Specifically, a drive gear of a second speed gear train and a drive gear of a fourth speed gear train are rotatably mounted on the counter shaft and a changeover mechanism is interposed between these drive gears. Further, driven gears of these gear trains are secured to the output shaft provided in parallel with the counter shaft. Further, the sub clutch is disposed at the end of the counter shaft corresponding to a mounting shaft of the shift gears (drive gears). The sub clutch is engaged or disengaged by hydraulic pressure on shifting gears.
In these prior automatic transmission described above, The sub clutch is disposed on the mounting shaft of the shift gears. Normally, a plurality of drive gears and a shift mechanism including changeover mechanisms and the like are disposed almost on allover the mounting shaft in an axial direction. Accordingly, in case where a sub clutch is mounted on the mounting shaft, in order to secure a space for accommodating the sub clutch on the mounting shaft, it is necessary to enlarge a longitudinal or axial size of the mounting shaft. Hence, an axial size of the transmission becomes larger than that of a prior type transmission. As a result, it becomes difficult to maintain the exchangeability with a prior type of a transmission (for example, manual transmission).
It is a primary object of the present invention to incorporate a sub clutch into a transmission case without increasing an axial size of the transmission. It is a further object of the present invention to provide a transmission having an exchangeability with a prior type of a transmission.
To achieve these objects, an automatic transmission having an input shaft, an output shaft, a main clutch for transmitting a power of an engine to the input shaft, shift gear trains for producing a specified gear ratio and a plurality of changeover mechanisms for automatically changing over the shift gear trains at shifting gears, comprises a plurality of mounting shafts for mounting respective shift gears of the shift gear trains, an intermediate shaft disposed on an axis other than axes of the mounting shafts and a sub clutch mounting on the intermediate shaft for variably controlling a torque transmitted from the input shaft to the output shaft when shifting gears.